he floor, its heavy pivot-base being riveted down to an iron
bed-plate. And the chair itself is not made of mahogany, as I had
supposed, but of an unknown metallic alloy that simulates the wood very
closely. Well, I was prepared for something like this.

"Another interesting point. The windows in the living-room face in a
southerly direction, and the sun is now every day getting a little
farther round, penetrating a little deeper, at every noon hour, into
the room. On the 21st it will cross the line, and at least one ray will
illumine a spot that for several months has not been touched by the
direct sunlight. What spot?

"It is nearing twelve o'clock, and as I sit in the big chair I can see
the bar of golden light creeping steadily onward. It reaches the chair,
and half-way around the pivot-base. Then the heavenly clock begins its
retrograde movement, and the ray of sunlight is forced to retreat. But
to-morrow it will come a little farther, and so again on the day after.

"Around the sash in the big window the architect has inserted a row of
glass bull's-eyes, a style of ornamentation suited to the semi-Oriental
tastes of William H. Seward Square. I go up and examine them closely.
They seem ordinary enough--but stop! The third from the bottom; it has
a peculiar depth and clearness. It might very well be a lens--a
burning-glass, to use the old-fashioned term. How close has the sun
drawn to this particular bull's-eye? To-morrow I will take note.

"March 20. At high noon the sun has reached within a hair's-breadth of
the third bull's-eye from the bottom. To-morrow it will surely shine
through my suspect, and if the latter be a true lens it will
concentrate, for several minutes, a high degree of heat at the
particular spot upon which its rays are focussed. That spot I have
found, by experiment, to be one of a series of small bosses set in the
pivot-base of the big chair. I applied the flame of a match and
immediately the metal boss began to soften. I understand now. The boss
is made of a fusible alloy that melts at a certain prearranged
temperature; it is simply a variation of the common safety plug used in
all the systems of mechanical protection against fire. At noon
to-morrow, March 21st, the rays of the sun will be concentrated by the
lens in the window-sash and will fall upon this boss of fusible metal.
The plug will melt, releasing a spring, let us say, and a train of
action will be set in motion.

"The precise n